The conventional method of constructing gravity driven roller conveyors involves two longitudinal spaced apart rails with rollers mounted between the rails. The rails can be angle shapes, channels or other standard structural profiles commonly available in steel or aluminum. The rails support the roller ends and the loads carried by the rollers. The rails can be supported by legs or other structures suitable to the installation. Rails can also support scanners, sensors and bumpers to control the motion of boxes, pallets or trays on the rollers.
Where a curved conveyor is required having a permanent configuration, the rails are rolled to follow the appropriate curvature. The spacing of rollers is varied along the length to locate rollers transverse to the curved rails. In some cases tapered rollers are used in curved conveyor sections which adds to the cost and complexity of manufacture. An alternative curved conveyor having a variable configuration has a scissor structure mounted on wheels that flexes to conform the conveyor to a curved path for temporary use such as loading and unloading trucks.
The complexity of manufacturing conventional curved conveyors has led to relatively high costs compared to a straight conveyor. To simplify manufacturing and reduce costs, conveyor manufacturers have produced curved conveyors with a predetermined constant radius of curvature.
For example, a circular conveyor section is manufactured to span an arc of 90 degrees or 45 degrees of a circular arc having a fixed radius of 5 feet, 10 feet or 15 feet. These prefabricated conveyor sections are combined with other curved sections and straight conveyors to produce a conveyor path that approximates the desired path. A similar approach is used in plumbing for example where standardized 90 degree and 45 degree sections are manufactured in various sizes to be used with straight sections to approximate the desired shape.
Due to standardization of the conventional curved sections, the radii of curvature are constant and so the roller mount spacing is constant and known but different on the inside rail and outside rail. However standardization enables the manufacturer to reduce costs through repetition in standardized jigs and allows the manufacturer to stock standardized parts in inventory for rapid sale and to make manufacturing predictable.
The conventional method of manufacturing a curved conveyor does not allow optimization of the conveyor path and restricts customization. A customer who requests a non-standard conveyor configuration that cannot be assembled from readily available standard pre-manufactured sections, will encounter significant cost increases. The manufacturer of a non-standard curved conveyor would be required to calculate and layout the locations of the conveyor roller mounts in a customized process which increases labour costs and lead time required for manufacture.
Although the conventional method of manufacturing can be adapted for complex curved shapes, the need for a customized design and manufacturing procedure makes the cost of complex curved shapes impractical. Accordingly complex shapes are assembled from standardized circular curved sections and straight sections to approximate the optimum or ideal configuration.
The ideal or optimum path for a curved conveyor would not include the abrupt changes in direction inherent in the use of standardized sections. For example if a box is conveyed down a straight line and then immediately into a circular curve, the box will continue in a straight line unless it collides with a bumper to retain the box in the curved section. The collision results in friction that slows the box down and repeated collisions can damage the box and bumper. A smoother transition could be provided using a spiral transition curve between the straight and circular sections, however a spiral curve requires more complex calculation and layout for bending the rails and spacing the roller mountings. Spiral transition curves are used in road design, railway track layout and roller coaster track design for the same purpose, namely, to avoid the uncomfortable lateral deceleration and bumping that would otherwise occur due to abrupt changes in direction.
Features that distinguish the present invention from the background art will be apparent from review of the disclosure, drawings and description of the invention presented below.